Cyclic nucleotide-gated channels serve as core components for Ca²⁺ signal encoding in guard cells

Tempo-spatial intracellular Ca²⁺ changes/oscillations mainly in cytoplasm and nucleoplasm are the primary mechanisms for the encoding and transmission of upstream stimulating signals to corresponding downstream responses, and the cytosolic Ca²⁺ signals are involved in numerous biological processes. External Ca²⁺ influx mediated by Ca²⁺ channels in the plasma membrane (PM) and the Ca²⁺ release from intracellular Ca²⁺ stores, such as vacuoles and endoplasmic reticulum (ER), respectively contribute to the majority and minority of Ca²⁺ for the generation of cytosolic Ca²⁺ signals, and the dynamic changes of PM Ca²⁺ channel activity directly control the rhythms of external Ca²⁺ influx and the subsequent cytosolic Ca²⁺ oscillations. Thus, the PM Ca²⁺ channels are the core components for Ca²⁺ signal encoding, but remain to be addressed for decades. Stomatal guard cell is an ideal plant cell model for deciphering Ca²⁺ signaling in plants, and more and more studies revealed that cyclic nucleotide-gated channels (CNGCs) play essential roles in Ca²⁺ signal encoding in guard cells. This minireview briefly summarizes the main recent advances in this field, highlights the core roles of CNGCs and underlying mechanism in guard cells, and discusses the possible remaining scientific questions and perspectives.